1. Field of the Invention
The present invention relates, in general, to technology for electrical feedback control for improving the sensor performance of typical gyroscopes, and, more particularly, to a system for implementing force rebalance control using an automatic gain control loop suitable for the design of small-sized and low power systems, such as Micro-Electro-Mechanical System (MEMS) gyroscopes.
2. Description of the Related Art
As well known to those skilled in the art, a gyroscope is a measurement sensor for measuring angular velocity, which is an inertial physical quantity existing in a rotating coordinate system, and representative examples thereof include a mechanical gyroscope and an optical gyroscope for detecting the difference between the traveling paths of light in a tachometer.
Small-sized and low power micro-gyroscopes using MEMS technology are currently being manufactured, and various application fields for use of the micro-gyroscopes have been proposed. Such a micro-gyroscope is applied to fields of inertial navigation systems used in airplanes, spacecraft, missiles, submarines, ships, etc., and the application fields thereof have extended to vehicle fields, such as vehicle attitude control, rollover detection, vehicle navigation, accident recording, collision avoidance, load leveling, and suspension control, consumer electronics fields, such as computer input devices, game controllers, virtual reality input tools, sports utility sensors, camcorders, and household robots, industrial electronics fields, such as self-controlled traveling, guide robots, oil hydraulic equipment, and attitude control, and small-sized flying object system fields, such as aerial electronics, antenna direction angle control, unmanned aerial vehicles, and light aircraft automatic landing devices. Recently, a rate-grade or tactical-grade gyroscope for angular velocity measurement used in typical control has been manufactured in the form of a micro-gyroscope using a semiconductor manufacturing process. Such a gyroscope having a micro-gyroscope form has characteristics such as small size, low power consumption, and mass production due to the manufacturing process thereof.
A vibratory gyroscope is characterized in that it employs a scheme for detecting Coriolis force applied to a mass body that vibrates in a plane perpendicular to an angular velocity input axis in a rotating coordinate system. In this case, the gyroscope can calculate the magnitude of an input angular velocity proportional to the Coriolis force by detecting a displacement signal induced by the Coriolis force.
FIG. 1 is a diagram showing an example of the operating principles of a typical gyroscope. As shown in the drawing, a mass body 10 vibrates according to dynamics in an X axis direction, causes Coriolis force, which is twice the angular velocity of the mass body, depending on an input angular velocity applied along a Z axis, and detects a displacement signal along a Y-axis, thus calculating the input angular velocity. In this case, the vibration amplitudes of driving displacement and detection displacement are determined using the modulus of elasticity of a driving axis spring 30 and a sensing axis spring 40, which support the mass body between the mass body and the framework 20 of the gyroscope.
Meanwhile, in the operating principles of the gyroscope, an open-loop detection method is disadvantageous in that the dynamic range of a sensor may be limited, non-linearity between input and output may be amplified, and bandwidth is greatly limited in an environment such as a vacuum, in which high frequency selectivity is required, but such a disadvantage can be overcome by applying a closed-loop type force rebalance control method of maintaining the displacement signal of a sensor in a uniformly balanced state.
The above-described closed loop-type force rebalance control realizes the force rebalance control of a gyroscope by utilizing a complicated robust control or adaptive control algorithm.
However, this is problematic in that, since complicated peripheral circuits, such as a microprocessor, are required, it is difficult to efficiently manufacture small-sized and low-priced sensors, and in that, since a method of completely suppressing the displacement signal of a detection axis caused by an input angular velocity is adopted, a very high control gain is required, thus making it difficult to implement circuits, or causing errors in force rebalance control.